1. Field of the Invention
The invention relates to a power feeding system and a vehicle, and the invention particularly relates to a power feeding system in which power is wirelessly fed from a power feeding installation to a vehicle by a power transmission resonator provided in the power feeding installation and a power receiving resonator provided in the vehicle resonating with each other via an electromagnetic field, and relates to a vehicle.
2. Description of the Related Art
Great attention has been focused on electrically powered vehicles, such as electric vehicles and hybrid vehicles, as environment-friendly vehicles. These vehicles incorporate an electric motor for producing drive force to propel the vehicle, and a rechargeable power storage for storing power to be supplied to the electric motor. Note that “hybrid vehicles” refer to vehicles incorporating an internal combustion engine as a motive power source in addition to the electric motor (or motors), vehicles further incorporating a fuel cell, in addition to the power storage, as a direct current power source for driving the vehicle, and so on.
Among the hybrid vehicles, a vehicle is known which allows charging of an in-vehicle power storage from a power source external to the vehicle, likewise with an electric vehicle. For example, a so-called “plug-in hybrid vehicle” is known which allows a power storage to be charged from a general household power supply by connecting, using a power cable, a plug socket located at a house with a charging inlet provided at the vehicle.
As a method for power transmission, attention has recently been focused on wireless power transmission not using power supply cords and/or power transmission cables. Three promising approaches of the wireless power transmission technique are known, i.e. power transmission using electromagnetic induction, power transmission using microwaves, and power transmission using the resonance method.
The resonance method is a contactless, or wireless, power transmission technique that causes a pair of resonators (e.g., a pair of resonant coils) to resonate with each other in an electromagnetic field (near field), thus transmitting power via the electromagnetic field. Using the resonance method, for example, power as high as several kW can be transmitted over a relatively large distance (for example, several meters).
For example, Japanese Patent Application Publication No. 2009-106136 (JP-A-2009-106136) describes a power feeding system that uses the resonance method to wirelessly feed power to a vehicle from a power feeding installation external to the vehicle.
In power feeding systems using the resonance method, such as the one described above, in order to achieve efficient power feeding from the power feeding installation to the vehicle, the input impedance at the resonance system that is constituted of a power transmission resonator in the power feeding installation and a power receiving resonator in the vehicle needs to be matched to the impedance at the power supply section from which power is supplied to the power transmission resonator. If these impedances are not matched to each other, the power reflected to the power supply device becomes large, and thus the power feeding is not efficient.
JP-A-2009-106136 does not specifically describe any concrete impedance adjustment (matching) method. Further, preferably, an impedance adjustment is accomplished with a structure as simple as possible.